As a conventional image processing method that composites or switches a plurality of input image signals, a process called “cross-fade” that switches image A to image B by adding baseband signals of two input images at a predetermined ratio, and changing the addition ratio along with the elapse of time, as shown in FIG. 13, is known. Also, an image processing method called “wipe” that switches baseband signals of two input images from image A to image B from the right to left of the screen along with the elapse of time, as shown in FIG. 14, is known. These image processes “cross-fade” and “wipe” are used upon, e.g., switching photographing scenes in a video camera as effects upon photographing (e.g., see Japanese Patent Laid-Open No. 2-301268).
As another image processing method that composites a plurality of images, an image processing method that extracts low- and high-frequency components from two input images, composites the high-frequency components of the two images, and composites the composited high-frequency components to the low-frequency components of one image so as to obtain a third image is known. Since the third image generated in this way contains the high-frequency components of the two images, a high-definition composite image can be obtained (e.g., see Japanese Patent Laid-Open No. 11-313205).
However, since the conventional image processes such as “cross-face”, “wipe”, and the like are executed using baseband signals such as luminance signals, color difference signals, and the like as image signals to be composited or replaced, the visual effects are limited.
Also, since the conventional image process that composites the high-frequency components of two images, and then composites the composited high-frequency components to the low-frequency components of one image aims at emphasizing the edge of one image generated by composition, such process is not suited as an effect upon switching seamless images such as a moving image.
Conventionally, a demand has arisen for a playback process faster than an actual recording time for the purpose of searching for desired contents within a short period of time, roughly recognizing the overall flow, and so forth upon playing back time-sequential image data such as moving image data.
An image processing apparatus having such high-speed playback function is available. In general, since a moving image is a set of images for one screen called a frame, a high-speed playback function is implemented by downsampled playback (e.g., by playing back recorded frames at intervals of several frames).
However, when such downsampled playback is made, as the playback speed increases (i.e., as the number of frames to be downsampled increases), a moving image to be played back becomes jerky, and the visual characteristics are not good.
As a high-speed playback method with improved visual characteristics, for example, Japanese Patent Laid-Open No. 7-162851 discloses a high-speed playback method which plays back only intra-encoded frames of encoded image data in which one intra-encoded frame and a plurality of inter-encoded frames alternately appear. Also, as described in Japanese Patent Laid-Open No. 7-162851, an intra-encoded frame is broken up into partial images called slices obtained by segmenting that frame in the horizontal direction, and one slice/frame is played back to attain quicker playback.
Furthermore, Japanese Patent Laid-Open No. 2001-352524 has proposed a method of generating a composite image for one frame from partial images of a plurality of successive frames, and playing back that composite image upon playing back a moving image encoded by MPEG at high speed.
The high-speed playback methods proposed by these references can display visually smooth motion of images even in the high-speed playback mode compared to simple frame downsampling. However, in these proposals, since a plurality of frame images are sliced (segmented) into rectangular patterns and a composite image for one frame is reconstructed by combining slice images of the respective frame images, the composite image includes images photographed at different times together.
For this reason, when a composite image is generated from images for four frames with inter-frame motions, as shown in FIG. 23, a composite image having deviations shown in FIG. 24 is obtained, and the reproduced image is visually not preferable.
In order to attain high-speed playback while generating such composite images, since a plurality of images must be read out, composited, and played back within a normal playback processing time for one frame, the load on the processing of the apparatus becomes heavier, and resources such as memories and the like are required in large quantities. For example, in the method proposed by Japanese Patent Laid-Open No. 2001-352524, data must be read out at a double speed in a double-speed playback mode.